Reserve one or more spare disks for every 10 disks that are part of a failure-tolerant volume, with a minimum of one spare disk for any disk group that contains failure-tolerant volumes.

Storage capacity is managed in subdisk units, but entire disks usually fail.Because entire disks fail, spare capacity reserved for recovering from disk failures should be entire disks whose capacity is at least as large as that of the largest disk in a failure-tolerant volume in the disk group.

When a disk fails, all non-failure-tolerant volumes having subdisks on it fail, and all failure-tolerant volumes become degraded.